1. Field of the Invention
This invention relates to an ink jet printing system and more particularly to a thermal drop-on-demand ink jet printing system.
2. Description of the Prior Art
A thermal drop-on-demand ink jet printing system is known in which a heater is selectively energized to form a "bubble" in the adjacent ink. The rapid growth of the bubble causes an ink drop to be ejected from a nearby nozzle. Printing is accomplished by energizing the heater each time a drop is required at that nozzle position to produce the desired printed image.
Depending on the frequency of operation and the array density, adjacent channels in a print head may affect each other thermally although this has not been a substantial problem with thermal drop-on-demand ink jet printing systems that are currently marketed. However, in applications where the number of channels in a thermal ink jet head is increased for high resolution, color and page printing, there is a requirement for higher drop rates and increased print density and these requirements require a solution to the problems caused by the resulting thermal cross-talk. The thermal cross-talk impedes print head performance since it creates an unsteady, non-uniform temperature field which can significantly alter the mechanism of bubble nucleation thereby leading to poor print quality.
U.S. Pat. No. 4,502,060 to Rankin et al shows a thermal ink jet printer in which barrier walls substantially surround the heater elements to define the capillary channels for feeding ink between a source and an orifice plate. The barrier walls also serve to maintain a separation between adjacent resistors to inhibit hydraulic cross-talk.
No prior art is known in which the print head structure is designed to diffuse heat away from the heater by specially designed thermal paths or to otherwise solve the thermal cross-talk problem.